The present invention relates generally to a heating, ventilating, and air conditioning system. More particularly, the present invention relates to a method and system for controlling a heating, ventilating, and air conditioning system.
Heating, ventilating, and air conditioning (HVAC) systems are used in both warm and cold climates to control the temperature of the air in a building or zone or zones within a building. An HVAC system typically includes a fan, a heating unit, and a cooling unit. The HVAC system may be operated in one of three modes: a heating mode to heat the enclosure, a cooling mode to cool the enclosure, or a ventilation mode to ventilate the enclosure.
Typically, a supply duct and a return duct connect the HVAC system to the zone or zones being conditioned. The fan operates to push air through the supply air duct and into the zone(s). Air is circulated through the zone(s) and back to the HVAC system through the return duct. The HVAC system may also include an outdoor air damper, commonly referred to as an economizer, that can be selectively opened to varying degrees, to allow outside air to mix with the return air to provide fresh air to the zone(s).
The operation of a HVAC system is governed by a control system, typically including a thermostat and associated programmable control hardware and software that sense parameters and control the various components of the particular HVAC system. The control system allows a user to select the operating mode of the HVAC system. In addition, the user may select a desired temperature for the zone or zones. The control activates the heating and cooling units in the HVAC system to maintain the desired temperature in the zone(s).
If the HVAC system is set to operate in the cooling mode and the temperature of the area exceeds the desired temperature, the HVAC system will activate the fan and the cooling stage. The fan blows air through the cooling unit and into the zone(s), thereby reducing the temperature of the air in the zone(s). Once the zone(s) are cooled to below the set temperature, the control device will turn off the cooling unit, or lower the stage of the cooling system, if it is a multi-stage system. Similarly, if the HVAC system is set to operate in the heating mode and the temperature of the zone(s) drops below the set temperature, the control device will activate the heating unit to warm the zone(s). The fan blows air through the heating unit and into the zone(s), thereby warming the zone(s). When the temperature rises above the desired temperatures the control device will shut off the heating unit, or lower the stage or capacity of the heating system, if it is a variable capacity or multi-stage system.
In certain HVAC systems, such as a constant volume HVAC system servicing a plurality of zones at a relatively constant volume of air flow, the unit will switch to the ventilation mode after the heating or cooling needs of the enclosure are satisfied. In the ventilation mode, the economizer is opened to allow outdoor air to enter the HVAC system. The fan mixes the outdoor air with the return air to ventilate the zone(s). The amount of air that is allowed through the economizer is governed by local building codes. According to these codes, the damper must typically be open at least 15% to 35%.
If there is a large temperature difference between the outdoor air and the air in the enclosure, the ventilation mode may cause discomfort within the zone or room. If, for example, the HVAC system is located in a hot climate where the outdoor temperature is much greater than the temperature of the zone(s), the mixture of the hot outdoor air with the air in the return duct results in supply air that is much warmer than the air in the zone. When this warm supply air enters the relatively cool enclosure, the flow of this warm air will be uncomfortable to persons near the supply vents and may cause hot spots in the room or zone. In addition, adding this warm supply air to the zone(s) will cause the temperature of the enclosure to rise rapidly. Similarly, if the outside air is very cold relative to the indoor temperature, the air supplied in the ventilation mode will be too cold and will cause similar problems in the opposite extreme.
In light of the foregoing there is a need for a method and system for controlling a heating, ventilating, and air conditioning system to control the temperature of the supply air in the ventilating mode.
Accordingly, the present invention is directed to a method and system for controlling a heating, ventilating, and air conditioning unit and maintaining the temperature of the conditioned air within a comfortable range. The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a system for conditioning air to be applied to one or more zones, so that the conditioned air applied to the zone(s) is maintained within a comfortable range. The system includes a conditioning unit that has a heating stage, a cooling stage, a fan, and an air damper, typically an economizer. The conditioning unit operates in an active mode where one of the heating stage and cooling stage is activated to condition air and in a ventilation mode where the fan moves supply air into the enclosure. Typically, the economizer is at least partially open during the operation of any of these modes. A supply air duct is provided for conducting the supply air from the conditioning unit to the zone or zones to be conditioned. A supply temperature sensor senses the temperature of the supply air. There is further provided a central control that activates one of the heating stage and cooling stage when the conditioning unit is in the ventilation mode and the temperature of the supply air is outside of a predetermined temperature range.
In another aspect, the invention is directed to a central control for an air conditioning system having a cooling stage, a fan, an air damper, and a temperature sensor. The air conditioning system operates in an active mode where the cooling stage is activated and in a ventilation mode where the fan is operated to provide supply air to zone(s). The temperature sensor senses the temperature of the supply air. The central control includes a thermostat to set an upper temperature setpoint and a lower temperature setpoint and associated hardware and instructions (such as software) to control the components of the system. The central control activates the cooling stage when the air conditioning system is operating in the ventilation mode and the temperature of the supply air is greater than the upper temperature setpoint.
In yet another aspect, the invention is directed to a central control for a heating system having a heating stage, a fan, an air damper, and a temperature sensor. The heating system operates in an active mode where the heating stage is activated and in a ventilation mode where the fan is operated to provide supply air to zone(s). The temperature sensor senses the temperature of the supply air. The central control includes a thermostat to set an upper temperature setpoint and a lower temperature setpoint and associated hardware and instructions (such as software) to control the components of the system. The central control activates the heating stage when the heating system is operating in the ventilation mode and the temperature of the supply air is less than the lower temperature setpoint.
In still another aspect, the invention is directed to a method of conditioning the air in one or more zones. The method involves operating a heating, ventilating, and air conditioning unit in a ventilation mode to provide supply air to the zone(s). The temperature of the supply air is sensed. When the system is in the ventilation mode, one of a heating stage and a cooling stage in said conditioning unit is activated to condition the supply air when the sensed temperature of the supply air is outside of a predetermined range.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.